1. Candidate Key:
It is a set of attributes that uniquely identifies a row. There may be more than candidate key and may be a combination of more than one attribute.
2. Primary Key:
A primary key is one of the Candidate Keys. It is a set of one or more attributes that can uniquely identify tuples in a relation.
3. Alternate Key:
The Candidate key that is not the primary key is called the alternate key.
4. Super Key:
A combination of a primary key with any other attribute or group of attributes is called a super key.
5. Foreign Key:
A single attribute or a set of attributes, which is a candidate key in another table, is called foreign key.
